This invention relates generally to storage and processing systems, and particularly to systems that may simultaneously record a plurality of components of an analogue data signal and then readout and process the stored data with a high degree of amplitude and phase registration.
Analogue storage and processing systems, such as those utilized in pulse doppler radars for example, determine a target's doppler frequency shift (velocity) by sensing the relative phase variation of successive pulses from a given range. in some prior art systems this doppler frequency determination is accomplished by demodulating the received radar signals and storing the in-phase component thereof along a first dimension of a storage medium which corresponds to target range. After a sufficient doppler history has been recorded in this manner, the storage medium is read out in a direction transverse to the first dimension to develop a read signal at each range interval that vary in frequency as a function of the doppler history of the received target signal.
However, in the just described prior art systems that record only the in-phase component of the received target signal, the maximum unambiguous doppler frequency is limited to one-half the pulse repetition rate of the radar transmitter. Since the maximum unambiguous doppler frequency is directly proportional to the maximum unambiguous target velocity that may be detected it would be desirable to have this unambiguous frequency as high as possible. It has been determined that if the received radar signal is demodulated by quadrature detectors and both the in-phase and quadrature components are stored and processed simultaneously, then an unambiguous doppler frequency up to the pulse repetition frequency of the radar may be realized. A storage and processing system that can accurately store, retrieve and process a plurality of simultaneously occurring signal components would double the velocity determination range of storage type pulse doppler radars and therefore be a great advancement in the signal processing art.
One possible mechanization for storing and processing the in-phase and quadrature radar data components would be to use separate parallel record and readout channels for each of the data components. However since the in-phase and quadrature radar signal components occur simultaneously, extreme care must be exercised so that these signals may be retrieved from storage and recombined without amplitudes or phase distortion degrading the accuracy of the desired doppler history.